Abstract
Ring Y chromosome is a very rare chromosomal aberration. The published mixed gonadal dysgenesis (MGD) patients with a ring Y chromosome are short in stature, but are not growth hormone (GH) deficient. We present the molecular cytogenetic and molecular characterization of ring Y chromosome mosaicism in a 10-year-old boy with MGD whose short stature could be explained by the high percentage of cells monosomic for the X-chromosome, but also by the presence of severe GH deficiency. The ring Y chromosome in our patient is a de novo structural aberration. The father's karyotype was normal.